The background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
Sulfur recovery units are commonly used in refineries, gas plants, and/or gasification plants, and with the increase of sourness of crude oil, gas, and/or coal, there is an increased demand on processing capacity of existing sulfur recovery units (SRUs) and/or demand for new SRUs.
Conventional Claus technology typically employs air as the combustion medium in the reaction furnace to facilitate the Claus reaction for sulfur recovery. While the nitrogen component of air does not participate in the Claus reaction, it occupies a significant amount of the equipment processing capacity, thus contributing to an increased equipment size. To reduce such disadvantage, at least some of the nitrogen can be replaced with oxygen, which allows for an increased acid gas processing capacity, and which in turn allows for smaller equipment size of new SRU/TGTU (tail gas treatment unit) facilities and increased acid gas processing capacity of existing SRU/TGTUs.
Use of such oxygen enrichment, however, is generally limited because the operating flame temperature of the burner increases with increased levels of oxygen and may reach or even exceed the design temperature of the refractory material. Therefore, flame temperature is typically the limiting factor controlling maximum tolerable oxygen levels in the oxygen enriched air, which in turn limits the increase in processing capacity of existing equipment. For example, H2S levels in SRU feed gases in refining plants are often in the range of 70% to 90%, and the flame temperature will usually reach or exceed refractory design temperature limitations at oxygen levels of 40-45% and above, limiting the increase in processing capacity to about 50-70% of the original equipment design capacity.
More recently, advances in oxygen enrichment have enabled high levels of oxygen enrichment to maximize increase in processing capacity of existing SRUs (e.g., 50%-200% of their original design capacity), and examples of such improvements are commercialized as SURE™ Technology (oxygen enrichment BOC, Guildford, Surrey, England) and COPE™ Technology (Claus Oxygen-based Process Expansion, Goar, Allison & Associates). The SURE technology uses a new reaction furnace/waste heat boiler (RF/WHB)to accommodate the extra oxygen needed while still limiting the amount of oxygen to be used in the existing reaction furnace for the flame to stay below the refractory design temperature limitation. As a consequence, a new reaction furnace/waste heat boiler (RF/WHB), and in most cases, a new sulfur condenser are needed in an existing SRU to achieve the desired processing capacity increase. The COPE technology employs a recycle cooled gas stream from the first sulfur condenser outlet back to the reaction furnace to so moderate flame temperature to below the design temperature limit of the refractory material. However, due to the relatively large quantities of recycle gas needed for moderating flame temperature, a new and bigger reaction furnace/WHB are often required to achieve a desired processing capacity increase.
Thus, even though several improvements have been made for oxygen enrichment in SRU/TGTUs, various drawbacks nevertheless remain. Among other things, relatively large volumes of recycle gas or new equipment to handle flame temperature increase are often economically unattractive. Consequently, there is still a need to provide improved oxygen enrichment in SRU/TGTU.